Hitherto, a communication system has been known which includes a device that is installed in a local area network (LAN), such as a home network, and a center system that monitors and controls the device in the LAN through a global network.
In the communication system, in some cases, a gateway (GW), which is a communication device for converting a communication protocol (communication rule) of packets transmitted and received between the device and the center system, is provided in the LAN.
For example, the communication protocol used by the center system for communication (a communication protocol used in the global network) is a hypertext transfer protocol (HTTP). In some cases, the communication protocol used by the device in the LAN for communication (a communication protocol used in the LAN) is determined based on the type of each device. In many cases, the communication protocol used by the device in the LAN differs from the communication protocol used by the center system.
The GW converts the communication protocol between the communication protocol of the packets transmitted and received between the device and a router in the LAN and the communication protocol used by the center system and the router in the LAN can transmit and receive packets between the device and the center system.
The GW includes a communication protocol module (hereinafter, simply referred to as a module) which performs a communication protocol conversion process. The module is a control element which is managed for each type of device (the communication protocol used by the device). The GW converts the communication protocol using the module corresponding to the device which is a packet transmission source or a packet transmission destination.
FIG. 31 is a diagram illustrating an example of the structure of a communication system 100.
As illustrated in FIG. 31, the communication system 100 includes a device installation area 110a, a device installation area 110b, and a center system 170.
The device installation area 110a is a device installation place, such as a home, and includes a device 120a-1, a GW 130a, and a router 140a. Similarly, the device installation area 110b includes devices 120b-1 and 120b-2, a GW 130b, and a router 140b. Hereinafter, when the devices 120a-1, 120b-1, and 120b-2 are not distinguished from each other, they are simply referred to as devices 120. When the GWs 130a and 130b are not distinguished from each other, they are simply referred to as GWs 130.
In the device installation area 110a, the device 120a-1 transmits and receives packets to and from the center system 170 using a communication protocol 121a. 
The GW 130a includes a module 131a. The GW 130a converts the communication protocol of the packets transmitted and received between the device 120a-1 and the router 140a between the communication protocol 121a and a communication protocol (for example, an HTTP) which is used by the center system 170 in a global network 160, using the module 131a. 
In the device installation area 110b, similarly, the devices 120b-1 and 120b-2 transmit and receive packets to and from the center system 170, using the communication protocols 121a and 121b, respectively. The GW 130b includes a module 131a corresponding to the communication protocol 121a of the device 120b-1 and a module 131b corresponding to the communication protocol 121b of the device 120b-2.
For example, a case in which the device 120a-1 transmits a packet which is generated in the format of the communication protocol 121a to the GW 130a will be described. The GW 130a converts the data format of the received packet into an HTTP format using the module 131a and transmits the packet to the center system 170. Then, the router 140a transmits (relays) the packet transmitted from the GW 130a to the center system 170 through the global network 160.
The center system 170 includes an application server 180 and a GW management server 190.
The GW management server 190 manages the devices 120 and the GWs 130.
The application server 180 provides the device 120 with an application service for monitoring or controlling the operation conditions of the device 120, based on the packet received from the device 120. The application server 180 generates a packet, such as commands or information, for the device 120 in an HTTP format and transmits the generated packet to the GW 130 through the global network 160.
When receiving the packet addressed to the GW 130a, the router 140a transmits (relays) the packet to the GW 130a. The GW 130a converts the data format of the received packet into a format of the communication protocol 121a using the module 131a corresponding to the device 120 (for example, the device 120a-1), which is a transmission destination, and transmits the packet to the device 120a-1 through the LAN 150a. 
Patent Literature 1: Japanese Laid-open Patent Publication No. 2000-312239
Patent Literature 2: Japanese Laid-open Patent Publication No. 2009-288859
The communication protocol of the packet transmitted by the device 120 is in one-to-one correspondence with a port number in, for example, an Internet protocol (IP). Therefore, the GW 130 can detect the communication protocol for communication with the device 120 from the port number.
However, in some cases, the module which can be installed in the GW 130 is limited due to restrictions in the hardware and software of the GW 130. In this case, even when the GW 130 detects a new device 120 in the LAN 150a or 150b, a module corresponding to the new device 120 is not arranged in the GW 130 and the communication of the new device 120 is likely to be limited.
In FIG. 31, an example in which the GW 130a does not have a software (module) download function and the GW 130b has a software download function will be described.
For example, when a device 120a-2 using the communication protocol 121b is added to the device installation area 110a, the GW 130a detects the addition of the new device 120a-2, but does not have a module corresponding to the communication protocol 121b. Therefore, the communication of the new device 120a-2 is limited because the GW 130a does not have a software download function, that is, due to software restrictions.
When a device 120b-3 using a communication protocol 121c is added to the device installation area 110b and the GW 130b detects the addition of the new device 120b-3, the GW 130b attempts to download a module corresponding to the communication protocol 121c. However, in some cases, the storage capacity of a storage device which stores the module of the GW 130b is insufficient. In this case, the GW 130b does not have the module corresponding to the communication protocol 121c due to hardware restrictions and the communication of the new device 120b-3 is limited.
As such, in the communication system 100, when the GW 130 does not have the module corresponding to the communication protocol used by the device 120, the communication of the device 120 is limited.